This document discusses different types of curves used in hill roads. There are two main types: horizontal curves and vertical curves. Horizontal curves include hairpin curves, which turn 180 degrees down a hillside, salient curves which curve outward on the hillside and are dangerous for traffic, and re-entrant curves which curve inward in a valley and provide better visibility. Vertical curves include summit curves which curve upwards to join roads of different grades, and valley curves which curve downwards and require sufficient sight distance at night. Design considerations for both types of curves include sight distance, vehicle comfort, and safety.

1. Types of Curve in Hill
Road
Prepared By
Dhrubajyoti Majumdar

2. Types of curves-Horizontal
• Hair Pin Curves
• Salient Curves
• Re-entrant curves

3. Hair Pin Curves
• changes its direction through an angle of
180 or so, down the hill on the same side
• conforms to the shape of a hair-pin
• located on hill side having the minimum
slope
• must be safe from the view point of land
slides and ground water
• Hair-pin bends with long arms and farther
spacing are always preferred

4. Salient Curves
• The curves having their convexity on the outer edges of a hill road are
called salient curves.
• The center of curvature of a salient curve lies toward the hill side.
• This type of curve occurs in the road length constructed on the ridge of a
hill.
• The bend so formed at the salient curve in hill road is known as corner
bend.
• Salient curves are very dangerous for fast-moving traffic.
• At such a curve or at corner bend, the portion of projecting hill side is
usually cut down to improve the visibility.
• The outer edge of the road at such a curve is essentially provided with a
parapet wall for protection of the vehicles from falling down the hill
slope.

5. Re Entrant Curves
• The curves having their convexity on the
inner edge of a hill road are called re-
entrant curve.
• This type of curve occurs in the road length
constructed in the valley of a hill.
• These curves are less dangerous as they
provided adequate visibility to the fast-
moving traffic. At such curves, the parapet
wall is provided only for safety of fast-
moving traffic.

7. Types of curves-
Vertical
• Summit Curve-
vertical curves with gradient
upwards.
• Valley Curve-
vertical curves with convexity
downwards

8. Summit Curves
• Objective :- To join 2 different
grades of roads with smooth
vertical curve, four different
conditions for formation summit
curve shown below –

9. Valley curve
• Objective – To join 2 different
grades of roads with smooth
vertical curve. Four different
conditions for formation summit
curve which are shown below -

10. Concepts behind
Summit Curve
• Design of summit curve on the basis
of sight distance.
• On summit curves, centrifugal force
acting outwards hence the springs of
vehicle is not compressed and
therefore passenger comfort is not a
issue.
• Design of summit curve as a square
parabola because the rate of change of
slope is decreasing always so more
sight distance available at the top of
curve.
Valley Curve
• In day time, no problem of any sight
distance but in night time head light
sight distance should be sufficient for
vehicle to stop before colliding with
object.
• In valley curves, the centrifugal force
will be acting downwards along with
the weight of the vehicle. This will
result in jerking of the vehicle and
cause discomfort to the passengers.